This grant will continue to look at the roles of mineral deficiencies and the vitamin D metabolites, especially 25-hydroxyvitamin D (25-OHD) in six areas: 1) In infants with early neonatal hypocalcemia, the effects of treatment modes on ionized calcium is under study. 2) In infants with late neonatal hypocalcemia the roles of hypomagnesemia and decreased PTH will be studied. 3) Mineralization and mineral homeostasis will be studied in premature infants fed: a) control formula or breast milk plus 400 I.U. vitamin D, b) a formula with increased calcium and phosphorous, c) the control formula plus 800 I.U. Vitamin D, and d) the control formula plus 2 micrograms/kg/day 25-hydroxycholecalciferol. 4) Linear growth retardation will be evaluated on long-term follow-up in premature infants previously studied and in infants undergoing treatment trials. 5) Dentition abnormalities and eruption delays will be looked for in these infants. 6) Autopsy samples from Sudden Infant Death Syndrome cases and controls are being analyzed for mineral content and quantitative bone histology is being performed. While in all areas hypercalcemia and 25-OHD deficiency will remain an area of focus, increased attention will be paid to deficiencies of phosphorous and magnesium and the trace elements, especially copper and zinc.